In order to obtain mass spectra of sample components developed and held on a TLC plate (Thin Layer Chromatography plate), a technique has been known which scrapes off the sample components, and after extracting and purifying them, introduces them into a mass spectrometer.
However, such a method of obtaining mass spectra involves the problems in that not only the method is extremely troublesome to practice and time consuming, information on the mixture state is completely lost if the sample components developed are a mixture.
Therefore, proposals have been made to introduce the TLC plate into a mass spectrometer and to obtain the mass spectra by SIMS (Secondary Ion Mass Spectrometry) or FAB (Fast Atom Bomberdment). In accordance with these proposals, while the TLC plate is moving in the direction of development of the sample components developed and held on the TLC plate, the TLC plate is bombarded by an accelerated and converged ion beam or by a fast speed atomic beam and ions obtained from the sample components are subjected to mass-analysis in order to obtain the mass spectra of the sample components. According to this method, the mass spectra can be obtained one after another and moreover, mass chromatogram can be obtained immediately by putting data in order and tracing the current value of a specific ion or the current value of all the ions.
When the sample components are bombarded by the ion beam or the fast speed atomic beam, the bombarded portion is locally sputtered so that occurrence of ions decreases. Therefore, a matrix such as glycerol is coated generally on the surface of TLC prior to the analysis in order that the sample components around the low ion portion migrate to it and the drop of the ion occurrence can be prevented.
Incidentally, the SIMS (or FAB) analysis method of the sample components on the TLC plate is described, for example, in "Journal of Biochemistry", Vol. 98, 1985, pp. 265-268.
As a result of experiments and studies, the inventor of the present invention has found out the following.
(1) Immediately after the primary beam bombardment, a phenomenon wherein large amounts of ions occur from the matrix surface (FIG. 1-II) or a phenomenon wherein ions hardly occur, (FIG. 1-II) on the contrary, takes place.
(2) If the primary beam bombardment is continued, the occurrence of ions changes drastically and about one or two minutes later, gets stabilized (FIGS. 1-I and 1-II). Though this time T till stabilization depends on the matrix to be added or the like, it hardly exceeds several minutes.
(3) It is assumed that the ion occurrence gets stabilized when electrical and physico-chemical equilibrium is attained.
(4) When the mass spectra are obtained by moving the TLC plate, a new surface is always bombarded by the primary beam. Accordingly, in this case, the mass spectra and mass chromatogram contain great changes and cannot be correct from the facts described above. In other words, FIG. 2-I shows the expected mass chromatogram while the mass chromatogram obtained in practice contains a great change as shown in FIG. 2-II and is not accurate.